System and method for reducing temperature variation during burn in

ABSTRACT

Systems and methods for reducing temperature variation during burn-in testing. In one embodiment, power consumed by an integrated circuit under test is measured. An ambient temperature associated with the integrated circuit is measured. A desired junction temperature of the integrated circuit is achieved by adjusting a body bias voltage of the integrated circuit. By controlling temperature of individual integrated circuits, temperature variation during burn-in testing can be reduced.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a Continuation of co-pending commonly ownedU.S. patent application Ser. No. 10/791,099, filed on Mar. 1, 2004,which is hereby incorporated by reference in its entirety. Co-pendingcommonly-owned U.S. patent application Ser. No. 10/334,272 filed Dec.31, 2002, entitled “Diagonal Deep Well Region for Routing Body-BiasVoltage for MOSFETs in Surface Well Regions” to Pelham and Burr, ishereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Embodiments in accordance with the present invention relate to systemsand methods for reducing temperature variation during burn in.

BACKGROUND

Highly integrated semiconductor devices, e.g., microprocessors,frequently dissipate a great deal of heat, particularly when operated atelevated temperatures and voltages to screen for defects during burn-inoperations. Such heat dissipation is deleterious during burn-inoperations, conventionally requiring complex and expensive heat sinking,e.g., water baths and/or liquid metal cooling, and expensive testchambers with very high cooling capacities.

SUMMARY OF THE INVENTION

Therefore, systems and methods for reducing temperature variation duringburn-in are highly desired.

Accordingly, systems and methods for reducing temperature variationduring burn-in testing are disclosed. In one embodiment, power consumedby an integrated circuit under test is measured. An ambient temperatureassociated with the integrated circuit is measured. A desired junctiontemperature of the integrated circuit is achieved by adjusting a bodybias voltage of the integrated circuit. By controlling temperature ofindividual integrated circuits, temperature variation during burn-intesting can be reduced.

In accordance with other embodiments of the present invention, anambient temperature in a region proximate to an integrated circuit ismeasured. Electrical power utilized by the integrated circuit ismeasured. A thermal resistance value for the integrated circuit isaccessed and a junction temperature of the integrated circuit iddetermined without direct measurement of the junction temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary arrangement of integrated circuitdevices configured for a burn-in operation, in accordance withembodiments of the present invention.

FIG. 2 illustrates a flow chart for a computer-implemented method ofreducing power during burn in testing, in accordance with embodiments ofthe present invention.

FIG. 3 illustrates an exemplary arrangement of integrated circuitdevices configured for a burn-in operation, in accordance with otherembodiments of the present invention.

FIG. 4 illustrates a flow chart for a computer-implemented method ofreducing power during burn in testing, in accordance with embodiments ofthe present invention.

FIG. 5 illustrates a flow chart for a computer-implemented method ofdetermining a junction temperature of an integrated circuit, inaccordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the present invention, systemand method for reducing temperature variation during burn in, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be recognizedby one skilled in the art that the present invention may be practicedwithout these specific details or with equivalents thereof. In otherinstances, well-known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

Notation and Nomenclature

Some portions of the detailed descriptions which follow (e.g., processes200, 400 and 500) are presented in terms of procedures, steps, logicblocks, processing, and other symbolic representations of operations ondata bits that can be performed on computer memory. These descriptionsand representations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. A procedure, computer executed step, logicblock, process, etc., is here, and generally, conceived to be aself-consistent sequence of steps or instructions leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated in a computersystem. It has proven convenient at times, principally for reasons ofcommon usage, to refer to these signals as bits, values, elements,symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present invention,discussions utilizing terms such as “storing” or “dividing” or“computing” or “testing” or “calculating” or “determining” or “storing’”or “measuring” or “adjusting” or “generating” or “performing” or“comparing” or “synchronizing” or “accessing’” or “retrieving’” or“conveying’” or “sending” or “resuming’” or “installing or “gathering”or the like, refer to the action and processes of a computer system, orsimilar electronic computing device” that manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage, transmission or display devices.

Embodiments in accordance with the present invention are described inthe context of design and operation of integrated semiconductors. Moreparticularly, embodiments of the present invention relate to systems andmethods for reducing temperature variation during burn-in testing ofintegrated circuits. It is appreciated, however, that elements of thepresent invention may be utilized in other areas of semiconductoroperation.

Although the following description of embodiments of the presentinvention will focus on coupling a body-bias voltage to pFETs (or p-typeMOSFETS) formed in surface N-wells via a conductive sub-surface regionof N-type doping when a p-type substrate and an N-well process areutilized, embodiments in accordance with the present invention areequally applicable to coupling a body-bias voltage to nFETs (or n-typeMOSFETS) formed in surface P-wells via a conductive sub-surface regionof P-type doping when an n-type substrate and a P-well process areutilized. Consequently, embodiments in accordance with the presentinvention are well suited to semiconductors formed in n-type materials,and such embodiments are considered within the scope of the presentinvention.

Burn-in operations to detect integrated circuit defects are generallyperformed at stressing temperatures, e.g., 150 degrees Celsius,stressing voltages, e.g., 1.5 times nominal operating voltage, and atlow operating frequencies, usually orders of magnitude slower thannormal operating frequencies. Under these conditions, leakage currenttends to dominate power consumption and heat production of theintegrated circuit device.

FIG. 1 illustrates an exemplary arrangement 100 of integrated circuitdevices configured for a burn-in operation, in accordance withembodiments of the present invention. Arrangement 100 comprises aplurality of integrated circuit devices under test, 101, 102 through N.The integrated circuits may be typically arrayed on a printed wiringboard 110, which may include sockets for accepting the integratedcircuit devices under test. Because it is desirable to operate theintegrated circuit devices under test at a stressing elevatedtemperature, wiring board 110 is typically placed in a temperaturechamber capable of temperature regulation, e.g., adding or removingheat, at high temperatures, e.g., 150 degrees Celsius. A typical burn-inchamber may comprise a plurality of similar wiring boards.

Wiring board 110 comprises a distribution network, e.g., wiring traces,to conduct electrical signals between various power supplies, testcontrollers and/or instrumentation and the integrated circuit devicesunder test. Wiring board 110 comprises an operating voltage (Vdd) supplydistribution network 141 and a test control distribution network 142. Itis appreciated that such wiring networks can be configured in a widevaried of well known networks, including bus, point-to-point, andindividual topologies in accordance with embodiments of the presentinvention.

Operating voltage supply 140 and test controller 150 are shown on wiringboard 110. Embodiments in accordance with the present invention are wellsuited to situating such components elsewhere within a test environment.For example, operating voltage supply 140 is frequently located outsideof a thermal chamber, and wired to a connector on wiring board 110. Testcontrol distribution network 142 couples a plurality of signals betweentest controller 150 and the integrated circuit devices under test.Similarly, operating voltage supply distribution network 141 couples aplurality of signals between operating voltage supply 140 and theintegrated circuit devices under test.

A test unit controller, which may or may not be apart of test controller150, typically stimulates the integrated circuit devices under test witha test pattern sequence and/or test commands and accesses a result.Embodiments in accordance with the present invention are well suited toa wide variety of test unit controllers and testing methods, including,for example, Joint Test Action Group (JTAG) boundary scan and arraybuilt-in self test (ABIST).

Operating voltage supply 140 provides voltage and current to operate theintegrated circuit devices under test, typically at a stressing voltage,e.g., 1.5 times nominal operating voltage for the integrated circuitdevices under test. Current consumption, particularly leakage currentconsumption, in most semiconductors increases with increasing operatingvoltage and with increases in operating temperature. Such currentincreases are generally exponential in nature, e.g., a ten percentincrease in operating voltage can cause a 100 percent increase inleakage current consumption. Operating the integrated circuit devicesunder test at a stressing elevated temperature also greatly increasestheir current requirements. As a deleterious consequence, operatingvoltage supply 140 must have a significantly greater current capacity tooperate the integrated circuit devices under test in comparison to acurrent capacity required to operate the same integrated circuit devicesunder nominal temperature and voltage conditions.

As a typical burn-in configuration can comprise several tens ofintegrated circuit devices under test per wiring board 110, and numerouswiring boards per chamber, the requirements placed upon operatingvoltage supply 140 can easily be measured in multiple kilowatts. Aprecision voltage supply capable of supplying such power and suitablefor testing integrated circuit devices can be prohibitively expensive.

Static power consumption in modern semiconductor processes, e.g.,processes with a minimum feature size of about 0.13 microns and smaller,is no longer a negligible component of total power consumption. Further,static power, as a percentage of total power, is tending to increasewith successive generations of semiconductor process.

For example, maximum operating frequency is generally proportional tothe quantity (1−Vt/Vdd), that is, one minus the threshold voltagedivided by the supply voltage (for small process geometries). As processgeometry shrinks, supply voltage (Vdd) typically also is decreased inorder to avoid deleterious effects such as oxide breakdown.Consequently, threshold voltage should also be decreased in order tomaintain or increase a desirable maximum operating frequency.Correspondingly, gate oxides are made thinner so that a gate canmaintain control of the channel. A thinner gate oxide leads to anincreased gate capacitance. Since “off” or leakage current of a CMOSdevice is generally proportional to gate capacitance, the trend to makegate oxides thinner tends to increase leakage current. As an unfortunateresult, the on-going decrease in semiconductor process size also leadsto an ever-increasing power consumption deriving from static powerdissipation. Further, essentially all of the electrical energy providedby operating voltage supply 140 is converted into heat by the integratedcircuit devices under test. As a deleterious effect, for most highlyintegrated circuits, the integrated circuits under test produce morethan enough heat to achieve a desired stress temperature, and thetemperature chamber is no longer required to provide such heat. In sharpcontrast, the temperature chamber must now be capable of removing vastheat loads, contributing to requirements for a very expensive chamber.

Further, conducting such vast amounts of heat out of the integratedcircuit die, through the integrated circuit packaging and into thetemperature chamber environment is problematic. Heat dissipationrequirements of highly integrated circuits, e.g., microprocessors,generally outpace heat dissipation capabilities of the integratedcircuit packaging under burn-in stress conditions. Consequently, veryexpensive “exotic” heat sinking arrangements, e.g., water baths andliquid metal cooling are conventionally employed to get the heat out ofintegrated circuits during burn-in testing.

Certain semiconductor devices have beet body biasing well structures tocontrol power consumption during operation. U.S. patent application Ser.No. 10/334,272 incorporated herein by reference and referenced above,describes such devices in more depth. In accordance with embodiments ofthe present invention, such body biasing well structures can beadvantageously utilized during burn-in operations to control particularparameters of a burn-in process.

Still referring to FIG. 1, positive bias voltage generator 120 iscoupled to positive bias voltage distribution network 121, which in turnis coupled to the integrated circuits under test. Positive bias voltagegenerator 120 provides a body-biasing voltage, e.g., zero to five volts,to n type wells disposed beneath pFET devices in the integrated circuitdevices under test. Such body biasing enables adjustment of thresholdvoltages of the pFET devices, for example, to reduce leakage current ofthe pFET devices.

In a similar manner, negative bias voltage generator 130 is coupled tonegative bias voltage distribution network 131, which in turn is coupledto the integrated circuits under test. Negative bias voltage generator130 provides a body-biasing voltage, e.g., −5 to zero volts, to p typewells disposed beneath nFET devices in the integrated circuit devicesunder test. Such body biasing enables adjustment of threshold voltagesof the nFET devices, for example, to reduce leakage current of the nFETdevices.

It is appreciated that such bias voltage distribution networks 121 and131 can be configured in a wide varied of well known networks, includingbus, point-to-point, and individual topologies in accordance withembodiments of the present invention. There may be a plurality of biasgenerators 120, 130 on wiring board 110, or bias generators may belocated off of wiring board 110, in accordance with embodiments of thepresent invention.

In general, bias voltage generators 120 and 130 are variable voltagesources. Their output voltage can be set (within a range) to a specificvalue. It is desirable, but not required, that such specific values beset digitally, e.g., by a command from test controller 150. Body biasingcurrents are typically on the order of low micro amps per integratedcircuit. Consequently, bias voltage generators 120 and 130 generally canbe relatively small and inexpensive voltage sources.

FIG. 2 illustrates a flow chart for a computer-implemented method 200 ofreducing power during burn in testing, in accordance with embodiments ofthe present invention. In block 210, an integrated circuit device istested to determine a set of body bias voltages which minimize leakagecurrent. In general, the testing will determine a unique n well voltageand a unique p well voltage for the integrated circuit device. It isappreciated that integrated circuits with a variety of power domains andbody biasing wells are well suited to embodiments in accordance with thepresent invention.

Advantageously, semiconductor packaging does not affect leakage current;therefore leakage current may be accurately measured on an unpackageddevice, e.g., on a wafer tester. As a beneficial consequence, ingeneral, no additional special test equipment or fixturing is requiredto perform block 210 within a typical semiconductor manufacturingprocess. Body bias voltages that minimize leakage current will generallybe determined outside of a burn-in process, for example during wafertesting. A set of body bias voltages that minimize leakage current maybe determined for an entire batch of integrated circuits, e.g., for awafer or for multiple wafers processes at the same time. Further,embodiments in accordance with the present invention are well suited todetermining body bias voltages that minimize leakage current forindividual integrated circuits.

In optional block 220, information of the set of body bias voltages,e.g., numerical representations of the voltages, is stored in a computerusable media. As previously described, block 210 and block 240, below,are well suited to being performed on different test equipment,physically separated, e.g., on different continents, at different times,e.g., weeks or months apart. Storing information of the set of body biasvoltages enables transmission and/or retrieval of this information foruse over distances in time and space.

In optional block 230, information of the set of body bias voltages isaccessed from a computer usable media. In accordance with embodiments ofthe present invention, the computer usable media of block 220 may differfrom the computer usable media of block 230. As is well known in thedata processing arts, information (data) may be copied and/ortransmitted in a variety of ways from media to media. In block 240, thebody bias voltages determined in block 210 are applied to an integratedcircuit during burn-in testing.

Advantageously, by controlling body bias voltages to minimize leakagecurrent during burn-in processing, power consumption and dissipation ofthe integrated circuits under test can be reduced by orders ofmagnitude. As a beneficial consequence of such greatly reduced powerconsumption, much less capable and much less expensive operating voltagesupplies and thermal chambers may be utilized for performing burn-intesting. Alternatively, greater numbers of integrated circuits can beburned in with existing equipment, thereby increasing throughput of aburn-in process. In addition, expensive exotic heat sinking arrangementsconventionally utilized with high function integrated circuits are nolonger required.

It is desirable to operate each integrated circuit at a specificjunction temperature during burn in, for example 150 degrees Celsius.Unfortunately, there will generally be a distribution of junctiontemperatures, “chip temperatures,” in a population of integratedcircuits undergoing burn in. For example, most temperature chambers areunable to maintain a precisely uniform ambient temperature at alllocations within the chamber. In addition, manufacturing variationsamong the integrated circuits under test contribute to differences inpower consumption, and hence differences in heat output between thevarious integrated circuits. Consequently, such differences in ambienttemperature and heat output contribute to variations in junctiontemperatures among the integrated circuits under test.

Conventionally, junction temperature variation has been addressed bymechanical temperature control of each integrated circuit, e.g., forcingheat into and drawing heat out of each integrated circuit in order toadjust its junction temperature to the desired temperature.Unfortunately, such conventional individual device temperature controlis mechanically complex and expensive. In addition, such structures forexternally applied heating and cooling generally have their ownrelatively large thermal mass, which greatly limits their ability torespond to changes in thermal requirements. Further, the coupling ofheating and cooling, as well as temperature measurements, are generallymade to integrated circuit packaging, rather than directly to junctions.Consequently, the junction temperature of the integrated circuit iscontrolled to an undesirable approximation.

Relation 1 below is an approximation of junction temperature of anintegrated circuit:Tjunction=Tambient+Pθi  (Relation 1)where T is temperature, P is power consumed by the integrated circuit.“θi” is the lumped thermal resistance of the integrated circuit packagecomprising, for example, a thermal resistance from the integratedcircuit to a coupled heatsink to ambient and/or a thermal resistancefrom the integrated circuit to a circuit board.

It is to be appreciated that the thermal resistance of the integratedcircuit package, θi, is highly consistent among similar integratedcircuits under test, and can be treated as a constant herein.

It is to be further appreciated that a desire of a burn-in process is tooperate the integrated circuits under test at a specific operatingvoltage, e.g., 1.5 times nominal operating voltage. Current requirementsof an integrated circuit, in general, are a function of attributes ofthat integrated circuit and the voltage applied. Hence, for a desirablespecific operating voltage, the power consumed by a particularintegrated circuit is essentially fixed for that integrated circuitunder the conventional art.

Beneficially, however, in accordance with embodiments of the presentinvention, power consumption of an integrated circuit can be adjusted byadjusting threshold voltage(s) of the integrated circuit, even ifoperating voltage of the integrated circuit is held constant. Thresholdvoltage(s) can be adjusted by adjusting body-bias voltage(s) supplied tobody-biasing wells disposed beneath active semiconductors of theintegrated circuit. Adjusting threshold voltage(s) of an integratedcircuit can make changes in, e.g., increase or decrease, the leakagecurrent of the integrated circuit, which is a significant component ofan integrated circuit's power consumption, especially during lowfrequency operation, for example, during a burn-in process.

In accordance with an embodiment of the present invention, junctiontemperature of an integrated circuit under test can be controlled bycontrolling the power consumed by the integrated circuit. The powerconsumed by the integrated circuit operating at a fixed operatingvoltage can be controlled by adjusting body biasing voltages to theintegrated circuit, which in turn influence leakage current of theintegrated circuit.

FIG. 3 illustrates an exemplary arrangement 300 of integrated circuitdevices configured for a burn-in operation, in accordance withembodiments of the present invention. Arrangement 300 comprises aplurality of integrated circuit devices under test, 101, 102 through N.The integrated circuits are typically arrayed on a printed wiring board310, which may comprise sockets for accepting the integrated circuitdevices under test. Because it is desirable to operate the integratedcircuit devices under test at a stressing elevated temperature, wiringboard 310 is typically placed in a temperature chamber capable oftemperature regulation, e.g., adding or removing heat, at hightemperatures, e.g., 150 degrees Celsius. A typical burn-in chamber maycomprise a plurality of similar wiring boards.

Wiring board 310 comprises an operating voltage supply 340, which may besimilar to operating voltage supply 140. Operating voltage supply 340provides voltage and current to integrated circuit devices under test101, 102, etc., though current monitors 301, 302, etc. Operating voltagesupply 340 is shown on wiring board 310. Embodiments in accordance withthe present invention are well suited to situating such componentselsewhere within a test environment. For example, operating voltagesupply 340 is frequently located outside of a thermal chamber, and wiredto a connector on wiring board 310.

In accordance with embodiments of the present invention, test controller350 provides significantly more function than test controller 150 (FIG.1). As will be discussed in more detail below, test controller 350 iscoupled to voltage supplies, current measurement devices and ambienttemperature sensor(s) in order to measure and control electricalparameters related to power consumption and temperature of theintegrated circuit devices under test.

Test controller 350 is desirably located on wiring board 310. However,due to various factors, e.g., the physical size and/or nature ofequipment used to implement test controller 350, embodiments inaccordance with the present invention are well suited to situating testcontroller 350 components elsewhere within a test environment, e.g., ona separate wiring board coupled to wiring board 310, or outside of athermal chamber. For example, if test controller 350 were implemented asa workstation computer, it would generally be impractical to place sucha workstation in a thermal chamber due to its size and operatingtemperature limits.

A test unit controller, which may or may not be apart of test controller350, typically stimulates the integrated circuit devices under test witha test pattern sequence and/or test commands and accesses a result.Embodiments in accordance with the present invention are well suited toa wide variety of test unit controllers and testing methods, including,for example, Joint Test Action Group (JTAG) boundary scan and arraybuilt-in self test (ABIST).

It is to be appreciated that current monitor 301 measures currentsupplied to integrated circuit 101, and that current monitor 302measures current supplied to integrated circuit 102. Each currentmeasurement is reported back to test controller 350, for example via adigital bus. It is appreciated that other wiring arrangements forreporting individual integrated circuit currents are well suited toembodiments in accordance with the present invention.

Test controller 350 is further coupled to operating voltage supply 340,such that test controller 350 has knowledge of the operating voltagesupplied to each integrated circuit under test. In general, theoperating voltage for each integrated circuit under test will be thesame. However, embodiments in accordance with the present invention arewell suited to a variety of operating voltages for the integratedcircuits under test.

Each integrated circuit under test is coupled to an associated positiveand/or negative body-bias voltage source. For example, integratedcircuit 101 is coupled to positive body-bias voltage source 321 andnegative body-bias voltage source 331. Likewise, integrated circuit 102is coupled to positive body-bias voltage source 322 and negativebody-bias voltage source 332. The body-bias voltage sources are in turncoupled to, and controlled by test controller 350.

With information of the operating voltage and current supplied to eachintegrated circuit under test, test controller 350 can determine thepower consumed by each integrated circuit under test. Ambienttemperature sensor 360 provides an ambient temperature measurement totest controller 350. There can be a plurality of ambient temperaturesensors associated with wiring board 310. For example, one ambienttemperature sensor per wiring board 310 provides a good approximation ofthe ambient temperature for integrated circuits under test on wiringboard 310. Alternatively, there could be an ambient temperature sensorassociated with, and in proximity to, each integrated circuit under teston wiring board 310.

Advantageously, it is generally less complex and less expensive tomeasure ambient temperature than to directly measure junctiontemperature of the integrated circuits under test. The number of ambienttemperature sensors utilized can be adjusted based upon costconstraints, accuracy requirements and understanding of thermalvariations within a particular chamber.

With information of power consumed by each integrated circuit under testand ambient temperature, the junction temperature of each integratedcircuit under test can be determined using Relation 1, above. If thecomputed junction temperature is not the desired junction temperature,test controller 350 can adjust the positive and/or negative body biasesof each integrated circuit under test to increase or decrease thresholdvoltage, and thus leakage current, and consequently power consumptionand in turn to achieve the desired junction temperature.

FIG. 4 illustrates a flow chart for a computer-implemented method 400 ofreducing power during burn in testing, in accordance with embodiments ofthe present invention. In block 410, power consumed by an integratedcircuit during a test process is measured. For example, current andvoltage to the integrated circuit can be measured.

In block 420, an ambient temperature associated with the integratedcircuit is measured. The ambient temperature should be more closelyassociated with the integrated circuit than a “set point” of atemperature chamber. For example, the ambient temperature can bemeasured by a single ambient temperature sensor on a wiring board, e.g.,wiring board 310 of FIG. 3, comprising an array of integrated circuits.Alternatively, the ambient temperature can be measured by an ambienttemperature sensor in close proximity to the integrated circuit.

In block 430, a body bias voltage of the integrated circuit is adjustedto achieve a desired junction temperature of the integrated circuit. Itis to be appreciated that body-biasing voltage can affect thresholdvoltages, which in turn affect leakage current which is a significantcomponent of integrated circuit power consumption. By adjusting, e.g.,increasing or decreasing, integrated circuit power consumption, thejunction temperature of an integrated circuit can be directlymanipulated. In combination with information of an ambient temperatureof the integrated circuit, a desired junction temperature can beachieved.

In this novel manner, a junction temperature of an integrated circuitcan be controlled without directly measuring the junction temperature ofthe integrated circuit. It is generally less complex and less expensiveto measure ambient temperature than to directly measure junctiontemperature of an integrated circuit. Further, systems to measure powerand control low current voltages are typically less complex and lessexpensive than creating individual thermal environments for largenumbers of integrated circuits. As a beneficial result, embodiments inaccordance with the present invention reduce temperature variationduring burn in with much less cost, much less complexity and withgreater reliability than the conventional practice.

FIG. 5 illustrates a flow chart for a computer-implemented method 500 ofdetermining a junction temperature of an integrated circuit, inaccordance with embodiments of the present invention. In block 510, anambient temperature in a region proximate to the integrated circuit ismeasured. The ambient temperature sensing device should be in the samethermal conditions as the integrated circuit.

In block 520, electrical power utilized by the integrated circuit ismeasured. Typically, such measurement is performed by measuring voltageand current supplied to the integrated circuit.

In block 530, a thermal resistance value for the integrated circuit isaccessed, for example, from computer memory. The thermal resistancevalue can be determined from packaging design information, but istypically measured during development of the integrated circuit and itspackaging.

In block 540, a junction temperature of the integrated circuit isdetermined. For example, using power, ambient temperature and thermalresistance, junction temperature can be computed using Relation 1,above.

In this novel manner, a junction temperature of an integrated circuitcan be determined without directly measuring the junction temperature ofthe integrated circuit. It is generally less complex and less expensiveto measure ambient temperature than to directly measure junctiontemperature of an integrated circuit. Further, power utilized by anintegrated circuit can be measured in a straightforward manner.Beneficially, embodiments in accordance with the present inventiondetermine a junction temperature of an integrated circuit in a lesscostly and less complex manner than under the conventional art.

Embodiments in accordance with the present invention, system and methodfor reducing temperature variation during burn in, are thus described.While the present invention has been described in particularembodiments, it should be appreciated that the present invention shouldnot be construed as limited by such embodiments, but rather construedaccording to the below claims.

1. A method of determining a junction temperature of an integratedcircuit, said method comprising: measuring an ambient temperature in aregion proximate to said integrated circuit; measuring electrical powerutilized by said integrated circuit; accessing a thermal resistancevalue for said integrated circuit, wherein said thermal resistance valueis dependent on packaging of said integrated circuit; and determining ajunction temperature of said integrated circuit by using at least saidmeasured ambient temperature, said measured power, and said thermalresistance value.
 2. The method of claim 1 wherein said determiningcomprises multiplying said thermal resistance value by said measuredelectrical power and adding said measured ambient temperature.
 3. Themethod of claim 1 wherein said measuring electrical power comprisesmeasuring current supplied to said integrated circuit.
 4. The method ofclaim 1 wherein said measuring electrical power comprises measuringvoltage supplied to said integrated circuit.
 5. The method of claim 1wherein said thermal resistance value is accessed from a computer usablemedia.
 6. A method of controlling power consumption of an integratedcircuit under test during burn-in testing, said method comprising:determining a junction temperature of said integrated circuit undertest; and adjusting a body bias voltage of said integrated circuit undertest to achieve a desired junction temperature of said integratedcircuit under test.
 7. The method of claim 6 wherein said determiningsaid junction temperature comprises: measuring power consumed by saidintegrated circuit under test; measuring an ambient temperatureassociated with said integrated circuit under test; and determining saidjunction temperature by using at least said measured ambienttemperature, said measured power, and a thermal resistance value.
 8. Themethod of claim 7 wherein said ambient temperature is measured for aregion comprising only said integrated circuit under test.
 9. The methodof claim 7 wherein said ambient temperature is measured for a regioncomprising more than one integrated circuit under test.
 10. The methodof claim 7 wherein said measuring power comprises measuring currentsupplied to said integrated circuit under test.
 11. The method of claim7 wherein said measuring power comprises measuring voltage supplied tosaid integrated circuit under test.
 12. The method of claim 7 wherein anoperating voltage of said integrated circuit under test remains fixedduring said measuring and said adjusting.
 13. The method of claim 6wherein said body bias voltage is individually controllable for saidintegrated circuit under test.
 14. The method of claim 6 wherein saidintegrated circuit under test comprises body-biasing well structures toaccept said body bias voltage.
 15. An apparatus for testing anintegrated circuit comprising: a power measuring device for coupling tosaid integrated circuit and for measuring power consumption of saidintegrated circuit; a body bias voltage supply for coupling to saidintegrated circuit and for providing a body bias voltage; an ambienttemperature sensor for determining an ambient temperature for a regionproximate to said integrated circuit; a test controller for coupling tosaid integrated circuit, said power measuring device, said body biasvoltage supply, and said ambient temperature sensor, wherein said testcontroller determines a junction temperature of said integrated circuitby using at least said measured power consumption, said measured ambienttemperature, and a thermal resistance value, and wherein said testcontroller causes adjustment of said body bias voltage to achieve adesired junction temperature.
 16. The apparatus of claim 15 wherein saidambient temperature is measured for a region comprising only saidintegrated circuit.
 17. The apparatus of claim 15 wherein said ambienttemperature is measured for a region comprising more than one integratedcircuit under test.
 18. The apparatus of claim 15 wherein said body biasvoltage is individually controllable for said integrated circuit. 19.The apparatus of claim 15 wherein said integrated circuit comprisesbody-biasing well structures to accept said body bias voltage.
 20. Theapparatus of claim 15 wherein said power measuring device comprises acurrent measuring device.